The goal of this study was to evaluate the mechanisms underlying Vernier acuity, over a range of spatial scales using
narrow-band Vernier stimuli and oblique masking. Specifically, the test stimuli consisted of a pair of vertical ribbons of horizontal
cosine grating with a vertical Vernier offset between the ribbons. These stimuli have two important advantages for studying
Vernier acuity: (1) they are relatively well localized in vertical spatial frequency, and (2) they are localized in their horizontal
extent (width). We measured the orientation, spatial frequency and width tuning of Vernier acuity over a wide range of ribbon
spatial frequencies, using a simultaneous oblique masking paradigm. Our masking results suggest that the mechanisms underlying
Vernier acuity are tuned to the orientation, spatial frequency and width of the ribbon stimuli. The peak of the bimodal orientation
tuning function varies systematically with the spatial frequency of the ribbon. The peak of the spatial frequency tuning function
varies systematically with both the ribbon spatial frequency, and the ribbon width (i.e. the grating length). A ‘template’ model,
in which the ‘mechanism’ is a windowed version of the stimulus is able to account for many features of the data, including results
which cannot be easily accounted for by standard multi-scale filter models. Specifically, the template model can account for: (i)
the bimodal orientation tuning function, (ii) the systematic variation in the peak of the orientation and spatial frequency tuning
functions with spatial frequency, and (iii) the systematic effect of ribbon width on spatial frequency tuning. © 2000 Elsevier
Science Ltd. All rights reserved.